US4700056A - Objective lens focus initialization system - Google Patents
Objective lens focus initialization system Download PDFInfo
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- US4700056A US4700056A US06/797,434 US79743485A US4700056A US 4700056 A US4700056 A US 4700056A US 79743485 A US79743485 A US 79743485A US 4700056 A US4700056 A US 4700056A
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- focus
- tracking
- objective lens
- track
- record carrier
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0945—Methods for initialising servos, start-up sequences
Definitions
- the present invention relates to optical data recording systems.
- the present invention is an objective lens focus initialization system for an optical data recording system.
- Optical data recording technology has developed to the point where it is commonly found in many consumer electronic products. Optical video disks and optical compact audio disks have, for example, become very popular. This technology is also being adapted to high density optical data recording and storage systems. With continued advances in this technology it is believed that optical systems of this type will be able to compete in terms of performance and cost with the magnetic data storage systems currently in widespread use.
- Optical data recording systems of the types referred to above include a record carrier, or disk, on which a single servo track is spirally positioned, or a plurality of servo tracks are concentrically positioned.
- a laser beam which is focused by an objective lens is used to write data onto, and to read data from, the servo tracks.
- Optical data recording systems also include a focus servo system for driving the objective lens about a focus axis, and maintaining the laser beam focused on a servo track.
- a tracking servo system is used to drive the objective lens along a tracking axis, and maintain the laser beam centered over a desired servo track.
- servo tracks are positioned extremely close to one another on a recording surface of the record carrier.
- Minimum spacing is determined by various optical and physical properties of the system. Servo track spacings on the order of 1.6 ⁇ m, for example, are common with current technology. Even though the servo tracks are placed extremely close together, their positioning with respect to the rotational axis of the record carrier is typically somewhat eccentric. In other words, the radial position of a given servo track from the rotational axis is not constant all the way around the record carrier. This eccentricity, or run-out, can range between 20 and 50 ⁇ m per servo track revolution.
- a focus initialization must be performed to bring the objective lens within focus capture range of the record carrier recording surface. Only after this initialization is performed is the focus servo system able to optically recognize the servo tracks and obtain information from them. Once the lens is positioned within focus capture range, the focus servo system is able to lock into focus, and the tracking servo system can lock onto a desired servo track.
- the focus initialization procedure is also performed when the focus servo system loses focus while in operation. Dirt or other flaws on the record carrier, or physical movement of the system, can, for example, cause focus loss.
- the focus servo system In order to initialize focus, the focus servo system must have some criterion, or basis, to verify placement of the lens within focus capture range of the record carrier recording surface.
- One commonly used technique is described in U.S. Pat. No. 4,446,546. With this technique, the lens is simply moved toward the record carrier from the far end of its travel limit furthest from the record carrier. A focus error signal is monitored during this period of motion and focus capture indicated when the lens is at such a position that the focus error signal is at a point between its peaks.
- Evaluating the focus error signal to verify focus capture does not always, however, produce optimum results.
- One common problem is the result of physical properties of the record carrier itself. Due to a high degree of sensitivity of the recording surface to dust, scratches and other physical imperfections, the recording surface is typically covered with a transparent protective layer. Notwithstanding its transparency, the protective layer will reflect radiation from the laser beam and produce stray or erroneous focus signals which known focus initialization systems can mistake for focus error signals. The focus servo system can use these stray signals to initialize focus on the protective layer, rather than the recording surface itself. In extreme cases, stray focus error signals can cause the objective lens to crash onto the protective layer. At best, the stray signals reduce overall performance of the focus initialization system.
- the present invention is a focus initialization system for positioning objective lens means within focus capture range of an optical record carrier recording surface in an optical data recording system. It is inexpensive due to minimal hardware requirements. The software required to implement the system is easily developed, and occupies little memory. Most importantly, the system is extremely fast and accurate, being insensitive to stray radiation reflections from the protective layer of the recording surface. This system is, therefore, particularly well suited for high density optical recording systems.
- an optical record carrier having a recording surface on which servo track portions are spaced about a rotational axis.
- the record carrier is rotated about its rotational axis by motor means.
- Objective lens means focus a beam of radiation along a focus axis oriented generally perpendicular to the record carrier recording surface, and collect modulated radiation from the record carrier.
- Detector means responsive to the objective lens means produce signals representative of modulated radiation collected by the objective lens means.
- Lens focus drive means drive and position the objective lens means along the focus axis in response to focus drive signals.
- Focus capture recognition means are responsive to the detector means and produce the focus drive signals.
- the focus drive signals are produced in a manner which causes the lens focus drive means to cyclically drive the objective lens means about a neutral position between peak offset positions along the focus axis.
- the focus drive signals also cause displacement of the peak offset positions from the neutral position to increase until the objective lens means is within focus capture range of the record carrier recording surface.
- the focus capture recognition means also determine whether the objective lens means is positioned within focus capture range of the record carrier recording surface at each offset position. Focus capture is recognized when the objective lens means sufficiently focuses the beam of radiation onto the recording surface to enable the detector means to produce signals representative of servo track portions thereon.
- the detector means includes a tracking error detector for producing a tracking error signal.
- the focus capture recognition means includes track crossing detector means, track crossing counter means, and focus capture control means,
- the track crossing detector means is responsive to the tracking error detector means and produces track crossing signals, preferably in the form of pulses, which are representative of relative motion along a tracking axis between the objective lens means and individual servo track portions of the record carrier.
- the track crossing counter means is responsive to the track crossing detector means and counts track crossing signals.
- the focus capture control means causes the lens focus drive means to operate in an open loop mode and drive the objective lens means to each offset position. Once the objective lens means is positioned at an offset position, the focus capture control means causes the lens focus drive means to operate in a low gain closed loop mode, and causes track counter means to count track crossings for a predetermined first time period. If at least a predetermined first number of track crossings are counted within the first time period, the focus capture control means causes the lens focus drive means to operate in a high gain closed loop mode, and causes the track crossing counter means to count track crossing signals for a predetermined second time period.
- the focus capture control means causes the lens focus drive means to operate in the open loop mode, and to drive the objective lens means to a succeeding offset position. Focus capture is recognized when at least the second number of track crossings are counted within the second time period.
- FIG. 1 is a block diagram representation of an optical data recording system utilizing the focus initialization system of the present invention.
- FIG. 2 is a perspective view of the top side of an optical record carrier illustrating servo track placement thereon.
- FIG. 3 is a magnified sectional view of the record carrier shown in FIG. 2 illustrating a recording surface and protective layer thereof.
- FIG. 4 is a graphic representation of the output of a focus error detector as a function of objective lens displacement from the record carrier recording surface.
- FIG. 5 is a graphic representation of an output of a tracking detector as a function of lens position along a tracking axis.
- FIG. 6 is a graphic illustration of cyclic objective lens displacement about a focus axis as produced by the focus initialization system of the present invention.
- FIG. 7 is a flow chart illustrating steps performed by the focus initialization sytem.
- Focus initialization system 10 of the present invention, optical data recording system 12, and their functional interrelationship, are illustrated generally in FIG. 1.
- Optical data recording system 12 includes record carrier 14 which is mounted on spindle 16 and is rotated about a rotational axis by motor 18.
- Information is optically encoded onto servo tracks 20 which are positioned on a recording surface of record carrier 14.
- Radiation beam 22 is produced by a source of radiation such as a laser (not shown), and focused onto record carrier 14 by objective lens 24.
- Objective lens 24 also collects from record carrier 14 modulated radiation representative of information stored within servo tracks 20. The collected modulated radiation is impinged upon an optical detector apparatus which includes focus error detector 26 and tracking error detector 28.
- Focus initialization system 10 includes lens focus drive circuit 30, lens tracking drive circuit 32, and focus capture recognition circuit 34.
- Lens focus drive circuit 30 is a servo drive system responsive to both focus error detector 26 and focus capture recognition circuit 34.
- Lens focus drive circuit 30 drives and positions objective lens 24 about an optical or focus axis 36. As shown in FIG. 1, focus axis 36 is oriented generally perpendicular to the recording surface of record carrier 14.
- Lens tracking drive circuit 32 is a servo drive system responsive to tracking error detector 28 and focus capture recognition circuit 34.
- Objective lens 24 is driven and positioned about tracking axis 38 by lens tracking drive circuit 32.
- tracking axis 38 extends in a radial direction from the rotational axis defined by spindle 16, and is perpendicular both to focus axis 38 and portions of servo tracks 20 which it crosses.
- Focus capture recognition circuit 34 is responsive to tracking error detector 28 and produces focus and tracking drive signals used by lens focus drive circuit 30 and lens tracking drive circuit 32, respectively, to bring objective lens 24 within focus capture range of a recording surface of record carrier 14.
- the focus drive signals produced by focus capture recognition circuit 34 cause lens focus drive circuit 30 to cyclically drive objective lens 24 about a neutral position between offset positions on focus axis 36. The displacement of objective lens 24 from the neutral position at the offset positions is increased until lens 24 is within focus capture range of the record carrier recording surface.
- focus capture recognition circuit 34 determines whether lens 24 is within focus capture range of the recording surface. Focus capture is recognized when lens 24 sufficiently focuses radiation beam 22 onto the recording surface of record carrier 20 to enable tracking detector 28 to produce signals representative of servo tracks 20.
- Record carrier 14 is commercially available in several different forms from a number of different manufacturers. In one form, as shown in FIG. 2, a plurality of servo tracks 20 are formed as closed rings and concentrically positioned about the rotational axis. Another form of record carrier 14, not shown, includes a single servo track 20 which is shaped in the form of a spiral. In both forms, individual arcuate portions of servo track(s) 20 are substantially concentrically positioned about the rotational axis, and radially spaced from one another. All references to "servo tracks 20" throughout the remainder of this specification apply to both forms.
- each servo track 20 is spaced approximately 1.6 ⁇ m from each other. Despite the small spacing, individual revolutions of servo tracks 20 on record carrier 14 are not perfectly circular. Rather, servo tracks 20 are somewhat eccentrically positoned on record carrier 14. The radial position of each servo track 20 with respect to the rotational axis therefore varies with angular position about record carrier 14.
- arcuate servo track portion 20A shown in FIG. 2, can be radially spaced from the rotational axis by a distance greater than or less than that of servo track portion 20B. This can be the case even though they are portions of the same servo track 20.
- This eccentricity, or run-out, is commonly between 20 and 50 ⁇ m.
- individual servo tracks 20 will appear to move in and out, in a radial direction, from the rotational axis when record carrier 14 is rotated by motor 18. This movement is graphically illustrated by line 40 in FIG. 2, and is generally parallel to tracking axis 38.
- FIG. 3 is a magnified sectional view of a portion of record carrier 14.
- record carrier 14 is formed of a radiation sensitive recording surface 42, and a protective layer 44.
- Servo tracks 20 are formed as grooves in recording surface 42, and are radially separated from each other by land portions 46. In the embodiment shown, servo tracks 20 have a width which is approximately equal to a width of land portions 46.
- Recording surface 42 of record carrier 14 is extremely sensitive to deterioration from scratches, dust, humidity, and other extraneous means.
- Protective layer 44 is formed of transparent material which is bonded to recording surface 42, thereby protecting surface 42 from these extraneous means. Plastic materials such as polyvinyl chloride are commonly used for protective layer 44.
- Focus error detector 26 (shown in FIG. 1) produces an electric signal which is representative of the relative distance between objective lens 24 and record carrier 14. In particular, focus error detector 26 produces a signal which represents the degree to which radiation beam 22 is or is not focused on the recording surface 42 of record carrier 14 by objective lens 24.
- a focus error signal produced by a commonly used quadrature-type focus error detector 26 is illustrated in FIG. 4. When objective lens 24 is far from focus, i.e. when the lens is converging radiation beam 22 to a focus point between the lens and the recording surface or beyond the recording surface, the output signal of focus error detector 26 is essentially zero.
- the focus error signal When objective lens 24 is at its focus position, and radiation beam 22 is focused on recording surface 42 of record carrier 14, the focus error signal has zero magnitude.
- Objective lens 24 is within focus capture range of the recording surface when it has a position between those represented by peaks 50 and 52 of the focus error signal.
- the portion of the focus error signal between peaks 50 and 52 is known as the linear region.
- Magnitude and polarity of the linear region of the focus error signal are linearly related to the distance and direction, respectively, of objective lens 24 from the focus position.
- Tracking error detector 28 (shown in FIG. 1) produces a tracking error signal representative of the direction and distance of objective lens 24, and therefore radiation beam 22, from individual servo tracks 20.
- a tracking error signal produced by a commonly used quadrature-type detector is illustrated in FIG. 5. As shown, the tracking error signal resembles a sine wave and has a magnitude of zero when a center of objective lens 24, and, therefore, radiation beam 22, is centered over servo tracks 20 and land portions 46. Each "zero crossing" is, therefore, representative of a center of a servo track 20 or a land portion 46. Peaks of the tracking error signal occur at transitions between land portions 46 and servo tracks 20.
- the zero crossings of the tracking error signal therefore, indicate or represent relative motion between objective lens 24 and servo tracks 20.
- the tracking error signal shown in FIG. 5, and its zero crossings, are produced by tracking error detector 28 only when objective lens 24 is within focus capture range of recording surface 42 of record carrier 14.
- focus initialization system 10 of the present invention does not make use of the focus error signal as a criterion or indicium for determining whether objective lens 24 is within focus capture range of the recording surface of record carrier 14. Rather, focus initialization system 10 uses the tracking error signal, and in particular, "track crossing" signals representative of relative motion between objective lens 24 and servo tracks 20 along tracking axis 38, to indicate focus capture. Focus initialization system 10 is therefore insensitive to stray focus error signals produced by reflections of radiation beam 22 from the protective layer 44 of record carrier 14.
- focus capture recognition circuit 34 is shown to include track crossing detector 60, track crossing counter 62, and focus capture control 64.
- Track crossing detector 60 is connected to receive the tracking error signal produced by tracking error detector 28.
- Track crossing detector 60 produces signals representative of relative motion between objective lens 24 and individual servo tracks 20.
- track crossing detector 60 produces a "track crossing" signal in the form of a pulse each time objective lens 24 passes over the center of either a land portion 46 or a servo track 20.
- the tracking error signal has zero magnitude at these instants, and each "zero crossing" of the tracking error signal therefore represents movement over a land portion 46 or a servo track 20.
- Track crossing detector 60 can be easily constructed from discrete or integrated circuit elements.
- Track crossing counter 62 is responsive to track crossing detector 60 and produces a signal representative of the number of track crossing pulses produced by track crossing detector 60.
- track crossing counter 62 is a digital counter which includes a clear input terminal 66.
- track crossing counter 62 produces a digital signal, on bus 67, representative of the number of track crossing pulses received from track crossing detector 60 after a CLEAR signal is received at clear input terminal 66.
- Digital counters of this type are commercially available.
- Focus capture control 64 is preferably a programmable control device, such as a microprocessor, which includes associated memory (not shown) for storing data, and timing means (not shown), for producing signals representative of elapsed time periods. Microprocessors of this type are commercially available and well known. As shown in FIG. 1, focus capture control 64 is responsive to track crossing counter 62 and receives from bus 67 a digital signal representative of a number of track crossing signals detected by track crossing detector 60. Focus drive signals, tracking drive signals, and a track crossing counter clear signal are all produced by focus capture control 64.
- the focus drive signals produced by focus capture control 64 include focus mode control signals representative of the mode of operation of lens focus drive circuit 30, and a focus position signal representative of a desired position of objective lens 24 on focus axis 36.
- the focus mode control signals including a first or LOW GAIN CLOSED LOOP focus mode control signal, a second or HIGH GAIN CLOSED LOOP focus mode control signal, and an OPEN LOOP focus mode control signal, are digital control signals which are propagated to lens focus drive circuit 30 on bus 68.
- the focus position signals are digital signals which are propagated to lens focus drive circuit 30 on bus 70.
- the tracking drive signals produced by focus capture control 64 include tracking mode control signals representative of the mode of operation of lens tracking drive circuit 32, and a tracking position signal representative of a desired position of objective lens 24 on tracking axis 38.
- the tracking mode control signals including a CLOSED LOOP tracking mode control signal, and an OPEN LOOP tracking mode control signal, are digital signals which are propagated to lens tracking drive circuit 32 by bus 72.
- the tracking position signals are digital signals which are propagated to lens tracking drive circuit 32 on bus 74.
- Focus capture control 64 also produces the track crossing counter CLEAR signal which is propagated to clear input terminal 66 of track crossing counter 62.
- Lens focus drive circuit 30, as shown in FIG. 1, includes digital-to-analog (D/A) converter 80, focus multiplexer 82, gain control 84, and focus actuator 86.
- D/A converter 80 is connected to bus 70 to receive the digital focus position signals from focus capture control 64.
- D/A converter 80 converts the digital focus position signals to analog form. The analog focus position signals are then supplied to focus multiplexer 82.
- Gain control 84 is responsive to focus error detector 26 and controls gain of the focus error signal received therefrom.
- gain control 84 is a passive voltage divider network formed by resistors 92 and 94. Resistor 92 has a first terminal connected to ground 98 and a second terminal connected to node 96. A first terminal of resistor 94 is connected to node 96, while a second terminal is connected to receive the focus error signal produced by focus error detector 26.
- gain control 84 shown in FIG. 1 produces a first or low gain focus error signal at node 96.
- the low gain focus error signal is supplied by gain control 84 at first output terminal 88.
- a second or high gain focus error signal is also produced by gain control 84.
- the high gain focus error signal is supplied by gain control 84 at second output terminal 90.
- the high gain focus error signal can be a replica of the focus error signal produced by focus error detector 26.
- Gain of the low gain focus error signal is less than that of the high gain focus error signal in the sense that it has a lower voltage change for a given amount of focus error than the high gain focus error signal.
- the low gain focus error signal is therefore less sensitive to focus errors than the high gain focus error signal.
- Gain control 84 can take other forms as well.
- Focus multiplexer 82 includes a first signal input terminal 100, a second signal input terminal 102, and a third signal input terminal 103.
- First signal input terminal 100 and second signal input terminal 102 are connected to receive the low gain focus error signal, and the high gain focus error signal, respectively, from gain control 84.
- Third signal input 103 is connected to receive the analog lens position signal from D/A converter 80.
- Focus multiplexer 82 also includes a signal output terminal 104 and a control input terminal 106. Control input terminal 106 is connected to bus 68 to receive the focus mode control signals from focus capture control 64.
- Focus multiplexer 82 is a digital device which functions much like a switch. In response to the particular mode control signal received, focus multiplexer 82 supplies the signal received at either the first, second, or third signal input terminals 100, 102, and 103, respectively, to output terminal 104. The selected signal is then propagated from output terminal 104 to focus actuator 86. Focus actuator 86 drives objective lens 24 along focus axis 36, and positions the lens at positions represented by the received signal. Focus actuator 86 is commercially available, and is typically an integral element of optical head assemblies.
- focus multiplexer 82 supplies the low gain focus error signal from gain control 84 to focus actuator 86.
- Lens focus drive circuit 30 is thereby operated in a LOW GAIN CLOSED LOOP focus mode, with focus actuator 86 driving objective lens 24 along focus axis 36 in response to the low gain focus error signal.
- a closed focus servo control loop is established since information representative of focus (the low gain focus error signal) is used to control position of objective lens 24. Since the low gain focus error signal is representative of both distance and direction of focus errors, focus actuator 86 uses this signal to maintain focus in the LOW GAIN CLOSED LOOP focus mode.
- focus multiplexer 82 supplies the high gain focus error signal from gain control 84 to focus actuator 86.
- Focus capture control 64 thereby operates lens focus drive circuit 80 in a HIGH GAIN CLOSED LOOP focus mode, with focus actuator 86 driving objective lens 24 along focus axis 36 in response to the high gain focus error signal.
- a closed focus servo control loop is again established since the high gain focus error signal is used to control the position of objective lens 24.
- Focus actuator 86 uses the high gain focus error signal to maintain objective lens 24 focused on a servo track 20.
- Lens focus drive circuit 30 has a higher sensitivity when operated in the HIGH GAIN CLOSED LOOP focus mode, and causes objective lens 24 to be more responsive to changes in the focus error signal than in the LOW GAIN CLOSED LOOP focus mode. Since the high gain focus error signal has a higher gain than the low gain focus error signal, lens focus drive circuit 30 more accurately maintains focus in the HIGH GAIN CLOSED LOOP focus mode than in the LOW GAIN CLOSED LOOP focus mode.
- focus multiplexer 82 propagates the analog focus position signal from D/A converter 80 to focus actuator 86.
- Lens focus drive circuit 30 is thereby operated in an OPEN LOOP focus mode, with focus actuator 86 positioning objective lens 24 at a position on focus axis 36 represented by the focus position signal.
- an open focus servo control loop is established since the focus error signal is not used to position objective lens 24. The focus servo control loop is therefore open between focus actuator 86 and focus detector 26.
- focus capture control 64 produces digital focus position signals which cause lens focus drive circuit 30, through focus actuator 86, to drive objective lens 24 along focus axis 36 in a cyclic motion.
- a mechanical lens suspension system (not shown) supports objective lens 24 in a neutral position above record carrier 14 when the lens is not being driven by lens focus drive circuit 30.
- focus capture control 64 causes focus drive circuit 30 to cyclically drive objective lens 24 about its neutral position between offset positions 110. Successive offset positions are on alternate sides of the neutral position. Displacement of each successive peak offset position 110, on both sides of the neutral position, preferably increases by a predetermined distance D with each successive cycle.
- D/A converter 80 is an eight bit device.
- Focus capture control 64 produces appropriate digital focus position control signals to divide the plus or minus 1mm movement of objective lens 24 into 255 sections. Displacement, D, of each successive offset position 110 from the neutral position in this embodiment therefore increases by approximately 7.8 ⁇ m. Focus capture control 64 is easily programmed to produce drive signals of these types.
- lens tracking drive circuit 32 is shown to include digital-to-analog (D/A) converter 120, tracking multiplexer 122, and tracking actuator 124.
- D/A converter 120 is connected to receive digital tracking position signals from focus capture control 64 on bus 74.
- D/A converter 120 converts the digital tracking position signals to analog form.
- Tracking multiplexer 122 includes a first signal input terminal 124, a second signal input terminal 126, a control input terminal 128, and a signal output terminal 130.
- First signal input terminal 124 is connected to receive the analog tracking position signal from D/A converter 120.
- Second signal input terminal 126 is connected to receive the tracking error signal from tracking error detector 28.
- Control input terminal 128 is connected to receive the tracking mode control signals produced by focus capture control 64.
- Tracking actuator 124 drives objective lens 24 along tracking axis 38, and positions the lens at positions represented by the received signals.
- Tracking actuator 124 is typically an integral element of an optical head assembly which includes objective lens 24.
- Tracking multiplexer 122 operates in a manner very much like that of focus multiplexer 82.
- OPEN LOOP tracking mode control signal is received at control input terminal 128, tracking multiplexer 122 supplies the tracking position signal from D/A converter 120 to tracking actuator 124.
- An open tracking servo control loop is established in the OPEN LOOP tracking mode.
- Lens tracking drive circuit 32 is thereby operated in an OPEN LOOP tracking mode, with tracking actuator 124 driving objective lens 24 along tracking axis 38 in response to the tracking position signals.
- Lens tracking drive circuit 32 positions lens 24, and a focus point of radiation beam 22, over a desired servo track 20 when operated in the OPEN LOOP tracking mode.
- Tracking multiplexer 122 supplies the tracking error signal received from tracking detector 28 to tracking actuator 124 when the CLOSED LOOP tracking mode control signal is received at control input terminal 128.
- Tracking drive circuit 32 is thereby operated in a CLOSED LOOP tracking mode, with tracking actuator 124 driving objective lens 24 along tracking axis 38 in response to the tracking error signal.
- a closed tracking servo control loop is established in the CLOSED LOOP tracking mode.
- the lens tracking drive circuit 32 thereby maintains objective lens 24, and a focus point of radiation beam 22, centered over a particular servo track 20.
- focus initialization system 10 The operation of focus initialization system 10 is best described with reference to FIGS. 6 and 7.
- the entire focus initialization procedure is preferably performed while objective lens 24 is stationarily positioned over record carrier 14.
- lens tracking drive circuit 32 While lens tracking drive circuit 32 is operated in its OPEN LOOP tracking mode, represented by step 140, focus capture control 64 will produce a tracking position signal representative of a particular position on tracking axis 38, as represented by step 142.
- Objective lens 24 is maintained at this tracking position throughout the focus initialization procedure.
- record carrier 14 is rotated by motor 18, servo tracks 20 will move back and forth along the tracking axis relative to objective lens 24, due to the eccentricity of their positioning on record carrier 14.
- the remaining steps of the focus initialization procedure bring objective lens 24 within focus capture range of the recording surface so that this motion can be detected by tracking detector 28.
- lens focus drive circuit 30 is next operated in the OPEN LOOP focus mode, with focus capture control 64 producing a focus position signal representative of a first offset position 110A. (See FIG. 6).
- Objective lens 24 is then driven to, and positioned at, offset position 110A by focus drive circuit 30.
- focus capture control 64 causes lens focus drive circuit 30 to operate in the LOW GAIN CLOSED LOOP focus mode, as represented by step 148.
- focus actuator 86 will drive objective lens 24 and maintain focus in response to the low gain focus error signal.
- the resulting movements, or excursions, of objective lens 24 from the offset positions, such as 110A, are illustrated in FIG. 6.
- Focus capture control 64 then allows objective lens 24 to settle for a delay period of preferably one to five milliseconds (step 150), after which time a CLEAR signal is produced and supplied to track crossing counter 62.
- Focus capture control 64 thereby causes track crossing counter 62 to count any and all track crossing signals produced by track crossing detector 60, for a predetermined first time period as represented by step 152 in FIG. 7.
- focus capture control 64 causes the first time period to be within a range of about 10 to 15 milliseconds.
- focus capture control 64 causes lens focus drive circuit 30 to operate in its OPEN LOOP focus mode, and to drive objective lens 24 to succeeding offset position 110B.
- offset position 110B is displaced from the opposite side of the neutral position as offset position 110A, by the same distance D.
- the initiation of this procedure is illustrated by step 154.
- focus capture control 64 will implement step 154 unless the first number of track crossings counted is within a range of about 2 to 5. Steps 144 through 154 are repeated at each successive offset position, with displacement of successive offset positions increasing, so long as less than the first number of track crossings are counted during the first time period. This procedure is, for example, illustrated in FIG. 6 by offset positions 110A through 110D.
- focus capture control 64 causes lens focus drive circuit 30 to operate in the HIGH GAIN CLOSED LOOP focus mode, as shown by step 158.
- focus actuator 86 will drive objective lens 24 and maintain focus in response to the high gain focus error signal. Due to the higher sensitivity of the high gain focus error signal, the excursions of objective lens 24 from an offset position (such as 110E) during the HIGH GAIN CLOSED LOOP mode are greater than those in the LOW GAIN CLOSED LOOP mode, as illustrated in FIG. 6.
- focus capture control 64 After switching lens focus drive circuit 30 into the HIGH GAIN CLOSED LOOP focus mode, focus capture control 64 allows objective lens 24 to settle for a second delay period, as represented by step 160, and then produces a CLEAR signal which is propagated to track crossing counter 62. Focus capture control 64 then causes track crossing counter 62 to count track crossing signals for a predetermined second time period as represented by step 162. In preferred embodiments, the second time period within a range of about 40 to 50 milliseconds.
- step 164 focus capture control 64 causes lens focus drive circuit 30 to again operate in the OPEN LOOP focus mode, and to position objective lens 24 at a succeeding offset position.
- step 164 is implemented unless a second number of track crossings within a range of 10 to 15 are counted during the second time period. Steps 144 through 164 are then repeated.
- the steps described above are illustrated by offset positions 110E and 110F in FIG. 6. At offset position 110E, for example, at least the first number of track crossings were counted during the first time period.
- step 166 in FIG. 7 focus capture is recognized.
- Focus initialization system 10 therefore utilizes a two step track crossing recognition procedure to obtain an indication of focus capture.
- the HIGH GAIN CLOSED LOOP focus mode is the regular closed loop focus mode in which lens focus drive circuit 30 operates once focus capture is recognized.
- Lens focus drive circuit 30, therefore, continues to operate in the HIGH GAIN CLOSED LOOP focus mode as shown by offset position 110G in FIG. 6.
- Focus capture control 64 can then operate lens tracking drive circuit 32 in either the OPEN LOOP tracking mode, or the CLOSED LOOP tracking mode as required for the particular operation being implemented.
- Focus initialization system 10 of the present invention requires very little specialized hardware. Other than gain control 84 and track crossing detector 60, all elements of focus initialization system 10 can be implemented by elements common to prior art data recording systems. Track crossing detector 60 is easily implemented by a Schmitt trigger or similar circuit. Circuits of this type are well known, small, and inexpensive. As shown in FIG. 1, gain control 84 can be implemented by two inexpensive resistors. Clearly, focus initialization system 10 is very inexpensive, despite the high degree of accuracy and high speed which can be achieved by its use. These characteristics are very important for economically practical optical recording systems.
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US06/797,434 US4700056A (en) | 1985-11-13 | 1985-11-13 | Objective lens focus initialization system |
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US06/797,434 US4700056A (en) | 1985-11-13 | 1985-11-13 | Objective lens focus initialization system |
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Cited By (24)
Publication number | Priority date | Publication date | Assignee | Title |
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US4878211A (en) * | 1986-05-26 | 1989-10-31 | Pioneer Electronic Corporation | Method and apparatus for correcting the loop gain of a servo loop in accordance with measurements during open-loop operation |
US4885733A (en) * | 1987-04-15 | 1989-12-05 | Pioneer Electric Corporation | Method of, and system for, detecting an excessive loading condition of multiple disks in a video disk apparatus |
US4890274A (en) * | 1985-04-16 | 1989-12-26 | Olympus Optical Co., Ltd. | Optical information recording and reproducing apparatus |
US4942564A (en) * | 1988-10-31 | 1990-07-17 | Hewlett-Packard Company | Servo system gain compensation method for magneto-optic disk drives |
US4975895A (en) * | 1987-08-28 | 1990-12-04 | Fujitsu Limited | Track servo control system for optical disk apparatus |
US4998233A (en) * | 1988-02-12 | 1991-03-05 | International Business Machines Corporation | Acquiring focus in optical systems using a focus error signal and a laser drive signal |
EP0420475A2 (en) * | 1989-09-25 | 1991-04-03 | Hewlett-Packard Company | Focus capture method for magneto-optic disk drives |
EP0423672A2 (en) * | 1989-10-14 | 1991-04-24 | Omron Corporation | Optical card processing apparatus |
US5042019A (en) * | 1987-08-07 | 1991-08-20 | Canon Kabushiki Kaisha | Method of and apparatus for seeking a desired track by counting track crossing signals which are detected within a predetermined time interval |
US5077719A (en) * | 1987-08-28 | 1991-12-31 | Fujitsu Limited | Optical disk access system |
US5189290A (en) * | 1989-10-14 | 1993-02-23 | Omron Corporation | Optical card processing apparatus using tracking error signals to determine proper card orientation |
US5363365A (en) * | 1992-01-14 | 1994-11-08 | Matsushita Electric Industrial Co., Ltd. | Optical pickup apparatus including a moveable pickup driver using a multiplexer for reducing the number of signal lines |
US5623463A (en) * | 1994-11-14 | 1997-04-22 | Daewoo Electronics Co., Ltd. | Method for determining a focusing control operation position in an opto-magnetic disc recording/reproducing apparatus |
US5694382A (en) * | 1994-04-05 | 1997-12-02 | Hewlett-Packard Company | Blank sector detection for optical disk drive |
US5703848A (en) * | 1994-04-05 | 1997-12-30 | Hewlett-Packard Company | Off track detection system for ruggedized optical disk drive |
US5745458A (en) * | 1994-04-05 | 1998-04-28 | Hewlett-Packard Company | Overlapped spin-up process for optical disk drive |
EP1246178A2 (en) * | 2001-04-02 | 2002-10-02 | Pioneer Corporation | Optical device for recording/reading optically recorded information |
US20030074150A1 (en) * | 2001-10-12 | 2003-04-17 | Peter Goldstein | Closed-loop focal positioning system and method |
US20040228013A1 (en) * | 2001-10-12 | 2004-11-18 | Intralase Corp. | Closed-loop focal positioning system and method |
US20070052456A1 (en) * | 2005-07-15 | 2007-03-08 | Watson Industries, Inc. | AGC circuit for the reduction of harmonics in the drive signal |
US20070106285A1 (en) * | 2005-11-09 | 2007-05-10 | Ferenc Raksi | Laser scanner |
US20090110374A1 (en) * | 2007-10-29 | 2009-04-30 | Funai Electric Co., Ltd. | Optical disc recording and playback apparatus |
US20100179519A1 (en) * | 2006-03-14 | 2010-07-15 | Amo Development, Llc | System and Method For Ophthalmic Laser Surgery on a Cornea |
US8937854B2 (en) * | 2001-01-25 | 2015-01-20 | Optical Devices, Llc | Servo processor receiving photodetector signals |
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Cited By (40)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4890274A (en) * | 1985-04-16 | 1989-12-26 | Olympus Optical Co., Ltd. | Optical information recording and reproducing apparatus |
US4878211A (en) * | 1986-05-26 | 1989-10-31 | Pioneer Electronic Corporation | Method and apparatus for correcting the loop gain of a servo loop in accordance with measurements during open-loop operation |
US4885733A (en) * | 1987-04-15 | 1989-12-05 | Pioneer Electric Corporation | Method of, and system for, detecting an excessive loading condition of multiple disks in a video disk apparatus |
US5042019A (en) * | 1987-08-07 | 1991-08-20 | Canon Kabushiki Kaisha | Method of and apparatus for seeking a desired track by counting track crossing signals which are detected within a predetermined time interval |
US4975895A (en) * | 1987-08-28 | 1990-12-04 | Fujitsu Limited | Track servo control system for optical disk apparatus |
US5077719A (en) * | 1987-08-28 | 1991-12-31 | Fujitsu Limited | Optical disk access system |
US4998233A (en) * | 1988-02-12 | 1991-03-05 | International Business Machines Corporation | Acquiring focus in optical systems using a focus error signal and a laser drive signal |
US4942564A (en) * | 1988-10-31 | 1990-07-17 | Hewlett-Packard Company | Servo system gain compensation method for magneto-optic disk drives |
US5113384A (en) * | 1989-09-25 | 1992-05-12 | Hewlett-Packard Company | Focus capture method for magneto-optic disk drives |
EP0420475A3 (en) * | 1989-09-25 | 1991-10-09 | Hewlett-Packard Company | Focus capture method for magneto-optic disk drives |
EP0420475A2 (en) * | 1989-09-25 | 1991-04-03 | Hewlett-Packard Company | Focus capture method for magneto-optic disk drives |
EP0423672A2 (en) * | 1989-10-14 | 1991-04-24 | Omron Corporation | Optical card processing apparatus |
US5189290A (en) * | 1989-10-14 | 1993-02-23 | Omron Corporation | Optical card processing apparatus using tracking error signals to determine proper card orientation |
EP0423672A3 (en) * | 1989-10-14 | 1991-06-05 | Omron Corporation | Optical card processing apparatus |
US5363365A (en) * | 1992-01-14 | 1994-11-08 | Matsushita Electric Industrial Co., Ltd. | Optical pickup apparatus including a moveable pickup driver using a multiplexer for reducing the number of signal lines |
US5745458A (en) * | 1994-04-05 | 1998-04-28 | Hewlett-Packard Company | Overlapped spin-up process for optical disk drive |
US5694382A (en) * | 1994-04-05 | 1997-12-02 | Hewlett-Packard Company | Blank sector detection for optical disk drive |
US5703848A (en) * | 1994-04-05 | 1997-12-30 | Hewlett-Packard Company | Off track detection system for ruggedized optical disk drive |
US5710748A (en) * | 1994-04-05 | 1998-01-20 | Hewlett-Packard Company | Off track detection system and method for ruggedized optical disk drive |
US5623463A (en) * | 1994-11-14 | 1997-04-22 | Daewoo Electronics Co., Ltd. | Method for determining a focusing control operation position in an opto-magnetic disc recording/reproducing apparatus |
US8937854B2 (en) * | 2001-01-25 | 2015-01-20 | Optical Devices, Llc | Servo processor receiving photodetector signals |
US9514777B2 (en) | 2001-01-25 | 2016-12-06 | Optical Devices, Llc | Servo processor receiving photodetector signals |
US9245569B1 (en) | 2001-01-25 | 2016-01-26 | Optical Devices, Llc | Servo processor receiving photodetector signals |
US9105281B2 (en) | 2001-01-25 | 2015-08-11 | Optical Devices, Llc | Servo processor receiving photodetector signals |
EP1246178A2 (en) * | 2001-04-02 | 2002-10-02 | Pioneer Corporation | Optical device for recording/reading optically recorded information |
US6865143B2 (en) | 2001-04-02 | 2005-03-08 | Pioneer Corporation | Optical device including a calibrating unit for calibrating a level adjusting unit |
US20020159344A1 (en) * | 2001-04-02 | 2002-10-31 | Pioneer Corporation | Optical device and optically recorded information recording/reading apparatus |
EP1246178A3 (en) * | 2001-04-02 | 2003-07-16 | Pioneer Corporation | Optical device for recording/reading optically recorded information |
US6751033B2 (en) * | 2001-10-12 | 2004-06-15 | Intralase Corp. | Closed-loop focal positioning system and method |
US7027233B2 (en) * | 2001-10-12 | 2006-04-11 | Intralase Corp. | Closed-loop focal positioning system and method |
US20030074150A1 (en) * | 2001-10-12 | 2003-04-17 | Peter Goldstein | Closed-loop focal positioning system and method |
US20040228013A1 (en) * | 2001-10-12 | 2004-11-18 | Intralase Corp. | Closed-loop focal positioning system and method |
WO2005106559A1 (en) * | 2004-04-20 | 2005-11-10 | Intralase Corp. | Closed-loop focal positioning system and method |
US7411465B2 (en) * | 2005-07-15 | 2008-08-12 | Watson Industries, Inc. | AGC circuit for the reduction of harmonics in the drive signal |
US20070052456A1 (en) * | 2005-07-15 | 2007-03-08 | Watson Industries, Inc. | AGC circuit for the reduction of harmonics in the drive signal |
US20070106285A1 (en) * | 2005-11-09 | 2007-05-10 | Ferenc Raksi | Laser scanner |
US11020272B2 (en) | 2005-11-09 | 2021-06-01 | Amo Development, Llc | Laser scanner |
US20100179519A1 (en) * | 2006-03-14 | 2010-07-15 | Amo Development, Llc | System and Method For Ophthalmic Laser Surgery on a Cornea |
US7870463B2 (en) * | 2007-10-29 | 2011-01-11 | Funai Electric Co., Ltd. | Optical disc recording and playback apparatus |
US20090110374A1 (en) * | 2007-10-29 | 2009-04-30 | Funai Electric Co., Ltd. | Optical disc recording and playback apparatus |
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